Manufacture of concentrated nitric acid.



K. BIRKELAND MANUFACTURE OF CONCENTRATED NITRIC ACID.

APPLICATION FILED JAN.13. I913.

1,Q36,662. Patentediug. 14AM? N m Q WED STATES PATENT onauon.

KBISTI AN IBIRKELAND, OE CHRISTIANIA, NORWAY, ASSIGNOR TO NORSK HYDRO- ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NORWAY.

MANUFACTURE CONCENTRATED NITRIC ACID.

To all whom it may concern:

Be it known that I, KRISTIAN BIRKnLANn, a subject of the King of 'Norwayyresiding at Christiania, Norway, have invented cers tain new and useful Improvements in "the of nitric acid and has for its object a process of concentrating the dilute acid Obtained by the absorption of nitrous gases more especially from such nitrous gases as are obtained by the trogen and oxygen.

According to the present invention the concentration of said dilute acid which usu ally has astrength of about 30 per cent. is effected by producing by means of the acid a nitrate of a metal and subsequently decomposingthe nitrate by treating it with superheated steam and condensing and further treating the vapors so obtained.

The dilute nitric acid is preferably transformed into a nitrate of a metal such as for instance zinc, lead or iron by dissolving an oxid of the metal in the acid and afterward. evaporating the solution to dryness in some.

Way or another. The nitrate may also be produced by treating a suitable ore or ore proiduct of the metal in question with the am In caf.ving out the further treatment of the nitrate so obtained the following operations and apparatus diagrammatically illustrated in the accompanying drawing may be'employed.

1 is a heating chamber, in which the nitrate is decomposed and steam introduced. The steam lntroduced' at 2, is preferably heated by passing through an electric flame furnace 3. The supply of nitrate to the heating. chamber at 4 and the discharge of the resulting oxid at 5 is preferably eflected in a continuous manner because in this case the'correct proportion=.-ibetween gases and steam is most easily maintained.

6. is a gasedecomposition chamber through Which the gases from the heating chamber l-areconducted'and it is heated to such a degree'that 6111} NO and no N0 is present in the gas. This is done because it .has

specification 01' Letters Patent. Application filed my 1a. 1913. Serial No.

such as will enable others skilled to which it appertains to make direct combination of air niprocess. hand 1s fairly Patented Aug. 14, 1917. 741,895.

proved to be of advantage for the subsegases rom the decomposition apparatus are conducted at 8 and where the nitric acid is formed and collected. .The condensed acid flows out at 9.

The gaseswhich leave the condensation plant are by ineans of a suitable blower 10 (of stoneware or the like) brought baclt 'into the decomposition chamber at 11 or at. some other point ahead of the condensation plant as at 12. To these gases there may first be added some oxygen and if nec essary also some steam. The oxygen, or the oxygen and. steam may be introduced through pipe 13. In the conduit leading from the condensation apparatus is suitably inserted a valve 14, which in case of the pressure becoming too high allows some gas to escape. This gas may be introduced into absorption towers 15 .for producing acid which may again be employed for producingnew amounts of nitrates. During the process impurities may accumulate in the gas circulating in the decomposition and condensation plant and in order to remove these impurities it may be of advantage from time to time to discharge the whole amount of gas through said valve.

Instead of again conducting the whole amount of gas containing nitrogen oXids leaving the condensation plant 7 into the decomposition plant 6. the gases" may be strongly cooled in the cooler 16 in order. to obtain liquid nitrogen tetroxid (N 0 discharged at 17 which is a valuable product for which there is a great demand. Several of ,those nitrates which maybe employed in connection with the present process contain in a solid state such as manufactured an amount of water su'iilcient to produce nitric acid with the other products of decomposition, without the addition of further amounts of steam. Such is the case for instance with nitrates of iron and zinc, which are both very suitable for the present The nitrate of lead on the other free from water. By treatmg the various easily decomposable nitrates in the manner to obtain nitric above describedfit is easy acid of the degree of concentration desired in each case for instance by regulating the amount of steam supplied or by heating the nitrates together with a suitable amount of water of crystallization or added water.

Instead of supplying the whole amount of water necessary for the formation of the nitric acid in the form of steam or in other ways during the decomposition of the nitrate, water vapor may be supplied to the nitric. acid. This process is based upon the observation that the mixture of nitrogenoxygen compounds, oxygen and n1tr1c ac1 d vapors formed by the decomposltion of n1- trates such as lead and zincnitrates are easily absorbed'in nitric "acid even if this acid has a temperature of 60 or C. By

the absorption, heat is evolved also and with gases having a temperature of 20 C., one.

may easily heat the whole amount' of acid to 70 C The absorption acid ata temperature of 50 C. contains practically no nitrogen oxids, while acid at a temperature of 10-20 C. may contain great amounts of tetroxid.

The process in question may be carried out as follows:

. An absorption tower for instance with a filling of quartz or a series of such towers are supplied from above at 19 with nitric,

acid and through these towers the nitrous gases are conducted, the working of the towers being so regulated, for instance by regulating the temperature of the gas current, that the acid at the foot of the tower at 20, where it is withdrawn, hasa temperature of about 100 C. at which temperature it is quite free from nitrogen oxids. If this process be employed in connection with nitrous gases obtained by the oxidation of air nitrogen and to which steam has been added it is unnecessary to maintain the discharge temperature so high to cause the absorption of the' nitrogen oxids but it may be suitable with regard to the concentration of the obtained acid.

The resulting acid is strongly cooled down and brought up to the top of the sam or another tower. In the upper part of the tower, where the temperature is low, the acid will he rirh in nitrogen oxids, but on passing downward the temperature of the same will be raised and the oxids will be given ofl and transformed into nitric acid.

If the nitrous gases before they are passed into the tower aretreated for the purpose of obtaining part of the oxids as nitrogen tetroxid, which is a valuable product of commerce pure oxygen will be obtained as a by product after the absorption tower. In the drawing 21 is the outlet for oxygen.

By means of the process above described unlimited quantities of nitric acid may be concentrated by the aid of a certain limited amount of a metal oxid.

I claim:

1. In the manufacture of concentrated nitric acid, the process which comprises reacting upon a substance containing metal capable of forming nitrate with dilute nitric acid, evaporating the solution and recovering the salt thereby eliminating the water of the dilute acid,-treating the salt with steam to decompose the salt to metal oxid and .a gas containing nitrogen combined with oxygen, transforming the peroxid (N0 content of said gas into nitric oxid (NO), reacting on the latter with nitric acid forming substances, and condensing the resulting nitric acid.

2. In the manufacture of concentrated nitric acid, theprocess which comprises rcacting upon a substance containing metal capable of forn'iing a readily decomposable nitrate with'dilute nitric acid, evaporating the solution and recovering the nitrate thereby eliminating the water of the dilute acid, treating the nitrate with steam, thereby producing metal oxid and liberating gas containing nitrogen combined with oxygen, converting the nitrogen peroxid (N0 content of the gas into nitric oxid (NO) reacting on the latter with steam and oxygen to form nitric acid, and condensing the resulting nitric acid.

3. In the manufacture of concentrated nitric acid, the process which comprises reacting upon a substance containing metal capable of forming nitrate with dilute nitric acid,-cvaporating the solution and recovering the salt thereby eliminating the water of the dilute acid. treating the salt with steam to decompose the salt to metalioxid and a gas containing nitrogen combined vwith oxygen, transforming the peroxid (N(),) content of said gas into nitric oxid (NO), reacting on the latter with nitric acid forming substances, condensing/the resulting nitric acid,

and strongly cooling the gaseous residuum to separate out nitrogen tetroxid.

4. In the manufacture ofconccutrated nitric acid. the process which comprises reacting upon a. substance containing metal capable of forn' ing nitrate with dilute nitric acid, evaporating the solution and recovering the salt tlierehyclimina ting the water ol.

thedilute acid, treating the salt with steam 1,2ee,ee2 a,

ter decompose .the salt to metal oxid Md a gas containing nitrogen combined with acid, and strongly cooling the gaseous residuum to separate out nitrogen tetiroxid,

absorbing the nitrogen compounds of the remaining gas and iecovering the resulting 18 free oxygen.

In testimony that I claim the foregoing as my invention, I have signed my name in presence of two subscribing Witnesses. 1

KRISTIAN BIRKELAND.

Witnesses:

GU'ITORMSLY, GUTH LINDsTROM.

Copies 0! this patent my be obteined'ter five cents each, by addressing the. Gommissicmer of Patents. Washington, D. G. 

